It does not follow, either, that psychoanalysis has never occupied itself at all with the non-sexual side of personality. The very distinction of the ego from sexuality has shown most clearly that the ego-impulses also pass through a significant development, which is by no means entirely independent of the development of the libido, nor does it fail to exert a reaction upon it. To be sure, we know much less about the evolution of the ego than about libido development, for so far only the study of narcistic neuroses has promised to throw light on the structure of the ego. There is extant the notable attempt of Ferenczi to construct theoretically the stages of ego development, and furthermore we already possess two fixed points from which to proceed in our evolution of this development. We do not dream of asserting that the libidinous interests of a person are from the outset opposed to the interests of self-preservation; in every stage, rather, the ego will strive to remain in harmony with its sexual organization at that time, and accommodate itself thereto. The succession of the separate phases of development of libido probably follows a prescribed program; but we cannot deny that this sequence can be influenced by the ego, and that a certain parallelism of the phases of development of the ego and the libido may also be assumed. Indeed, the disturbance of this parallelism could become a pathological factor. One of the most important insights we have to gain is the nature of the attitude which the ego exhibits when an intensive fixation of its libido is left behind in one stage of its development. It may countenance the fixation and accordingly become perverse or, what amounts to the same thing, become infantile. Or it may be averse to this attachment of the libido, the result of which is that wherever the libido is subject to _fixation_, there the ego undergoes _suppression_. In this way we reach the conclusion that the third factor of the etiology of neuroses is the tendency to _conflict_, upon which the development both of the ego and libido are dependent. Our insight into the causation of the neuroses has therefore been amplified. First, the most generalized factor, self-denial, then the fixation of the libido, by which it is forced into certain directions, and thirdly, the tendency to conflict in the development of the ego, which has rejected libidinous impulses of this kind. The state of affairs is therefore not so confused and difficult to see through, as you may have imagined it to be in the course of my explanation. But of course we are to discover that we have not, as yet, reached the end. We must add still a new factor and further analyze one we already know.